Recent developments in semiconductor technology include the complementary metal-oxide-semiconductor (CMOS). CMOS is a technology employed in constructing integrated circuits, producing semiconductor devices having a wide variety of uses in electronic components. These uses can include, for instance, microprocessors, microcontrollers, static random access memory, and other digital logic circuits. Analog uses include data integrators, and integrated transceivers employed in electronic communication, as well as for image sensors.
One particular type of image sensor leveraging CMOS technology is the CMOS image sensor. A CMOS image sensor can be incorporated into a System-on-Chip (SoC). As such, the SoC can integrate various components (e.g., analog, digital, . . . ) associated with imaging into a common integrated circuit. For instance, the SoC can include a microprocessor, microcontroller, or digital signal processor (DSP) core, memory, analog interfaces (e.g., analog to digital converters, digital to analog converters), and so forth.
Visible imaging systems utilizing CMOS imaging sensors can reduce manufacturing costs for such systems, reduce power consumption of an electronic device, and reduce electronic noise, while improving optical resolution. For instance, cameras can use CMOS imaging System-on-Chip (iSoC) sensors that efficiently marry low-noise image detection and signal processing with multiple supporting blocks that can provide timing control, clock drivers, reference voltages, analog to digital conversion, digital to analog conversion and key signal processing elements. High-performance video cameras can thereby be assembled using a single CMOS integrated circuit supported by few components including a lens and a battery, for instance. Accordingly, by leveraging iSoC sensors, camera size can be decreased and battery life can be increased. The iSoC sensor has also facilitated the advent of more advanced optical recording devices, including dual-use cameras that can alternately produce high-resolution still images or high definition (HD) video.
An image sensor converts an optical image into an electronic signal. This electronic signal can then be processed and reproduced, for instance on a display screen. Typically, the image sensor comprises an array of many active pixels; each active pixel comprising a CMOS photodetector (e.g., photogate, photoconductor, photodiode, . . . ) controlled by circuits of digitally controlled transistors. The CMOS photodetector can absorb electromagnetic radiation in or around the visible spectrum (or more typically a subset of the visible spectrum—such as blue wavelengths, red wavelengths, green wavelengths, etc.), and output an electronic signal proportionate to the electromagnetic energy absorbed.
Electronic imaging devices, such as digital cameras and particularly video recorders, capture and display many optical images per second (e.g., 30 per second, 60 per second, 70 per second, 120 per second, . . . ), equal to the optical frame rate of the imaging device. Capturing a single image in a single frame time involves multiple operations at the CMOS pixel array and readout circuit. One mechanism for image capture is referred to as a rolling shutter. As an example, rolling shutter operations can include capture and convert (e.g., capture light information and convert to electrical information), readout, and reset operations. Some frames can be constructed so that the capture and convert operation, and the reset operation are performed in a single reset cycle, for instance, with reset of a prior frame occurring at a beginning of the reset operation, and capture and convert of a current frame occurring at the end of the reset operation. Thus, alternating reset and readout cycles can clear the CMOS photodetector array, capture a new image, and output the captured image for processing.
Conventional images sensors communicate with external components on the iSoC to control the image sensor operations (e.g., readout operations, reset operations, etc.). Common external components on the iSoC include a processor, serial peripheral interface (SPI), and a field programmable gate array (FPGA) to maintain the image sensor operations. Since timing in the image sensor is often very specific, the FPGA communicates with the image sensor using real time signals. The processor and SPI communicate with the image sensor using non-real time signals. However, the non-real time signals do not allow precise control of timing. For example, the image sensor may need to read out data five clock cycles after the rising edge of a synchronization signal. If the data is not read out five clock cycles after the rising edge of a synchronization signal, the image sensor operations can be hindered. Since real time signals and non-real time signals are used to communicate to the image sensor, fine control of timing is often very difficult. As a result, complicated interactions between the non-real time signals and the real time signals are used to control the image sensor operations. Consequently, conventional image sensors do not allow versatile implementation for multiple applications and/or complex image sensor operations.